1. Field of the Invention
The present invention generally relates to a spool valve having a spool that slides within a valve housing in a longitudinal direction. For example, the present invention relates to damper means that damps vibration of the spool in the longitudinal direction. The present invention, for example, relates to an art used in a hydraulic control valve of an automatic transmission, and the like.
2. Description of Related Art
As an example of a related spool valve, which provides a damper function for a spool, JP-A-2006-112514 describes an solenoid operated hydraulic control valve carried in an automatic transmission.
The solenoid operated hydraulic control valve of JP-A-2006-112514, is of the kind shown, for example, in FIG. 6. That is, a spring chamber restrictor J3 with a small passage area is formed in a drain port or similar external communication passage that provides communication between a spring chamber J2, where a return spring J1 is provided, and an exterior (low pressure side) such that vibration of a spool J4 in a longitudinal direction is controlled (limited).
Typically, the solenoid operated hydraulic control valve is made by combining a spool valve J5 and a solenoid J6. The resulting valve controls a longitudinal position of the spool J4 by driving the solenoid J6 with a drive signal having a controlled duty cycle. As a result, the output oil pressure of the spool valve J5 is controlled.
In recent years, the need for improved response of a gear change of an automatic transmission has increased.
When conventional solenoid operated hydraulic control valve directly drives the spool valve J5 by the solenoid J6, disadvantages are apparent. For example, when the output of the solenoid J6 is increased in order to improve a response, the corresponding increase in the vibration of the spool J4 resulting from the duty cycle frequency applied to the solenoid J6 has a disadvantageous effect.
Thus, it is desired to raise a damper effect by combining new damper means to the existing damper means (spring chamber damper means) of the spring chamber J2 and the spring chamber restrictor J3.
That is, development of new damper means different from the existing damper means is desired.
It should further be noted that the spring chamber J2 communicates with the exterior or low pressure side via the spring chamber restrictor J3 as above.
As shown in FIG. 7A, in a first case, where an oil level L of the exterior (low pressure side) is higher than (above) the spring chamber J2, and also in another case, where the spring chamber restrictor J3 is formed in an upper end of the spring chamber J2, an interior of the spring chamber J2 becomes filled with oil.
However, in other structures, for example, as shown in FIG. 7B, due to an oil passage layout, the oil level L of the exterior (low pressure side) may be lower than (below) the upper end of the spring chamber J2 (e.g., the oil level L is positioned at intermediate part of the spring chamber J2 in an up-down direction), or, the spring chamber restrictor J3 may be located lower than the upper end of the spring chamber J2 such that the oil level L is positioned at the intermediate part of the spring chamber J2 in the up-down direction. In these cases, an air pocket, where air that enters at the time of assembly may be captured, is formed in the spring chamber J2 located higher than the spring chamber restrictor J3.
Because the spring chamber J2 is a chamber, which receives the return spring J1, the spring chamber J2 has a substantially large volume. Therefore, when air is captured in the spring chamber J2, the volume of the air pocket will also become large. Thus, when the air pocket having the large volume is formed in the spring chamber J2, air compression takes place within the spring chamber J2. Therefore, the damping effect of the spool J4 may become disadvantageously degraded.